The exact cause of the gas leaks is not clear, but reports say the blasts were caused by ruptured pipelines.

Images of the scene showed major fires, upturned vehicles, bodies covered in debris and streets split in two.

The explosions happened late on Thursday night, with witnesses reporting huge fireballs soaring into the air. Taiwan's premier said there were at least five blasts.

"The local fire department received calls of gas leaks late Thursday and then there was a series of blasts around midnight affecting an area of two to three sq km [one sq mile]," the National Fire Agency said in a statement.

"I saw lots of cars and motorcycles with engines all over on the road, and doctors checking if bodies were dead or alive," eyewitness Chen Guan-yuan, who was at the scene shortly after the blast, told the BBC.

"Because the explosion range is so far so it's really difficult to handle this situation immediately," Mr Chen said, adding that the blasts "caused a long-range hole, like a huge cave".

Image copyrightAFPImage caption
The explosions split roads in two and threw vehicles into the air

Image copyrightAFPImage caption
The blasts ripped through the southern city of Kaohsiung late on Thursday

Four firefighters who were investigating reports of a gas leak were said to be among the dead.

People in the area were evacuated to schools as teams battled the blazes. By Friday morning most fires were reported to have been extinguished.

Firefighters were still trying to see if people were trapped under the rubble, the BBC's Cindy Sui in Taipei reported.

The exact cause of the blasts had not yet been identified but several petrochemical companies had pipelines running along the sewage system in the district, our correspondent added.

"The cause of the gas leak is still not clear at this moment. We suspect the leaked gas could be propylene," said Economic Affairs Minister Chang Chia-chu.

Cindy Sui, BBC News, Kaohsiung

The area where the explosions happened is just a short distance from the Kaohsiung City Hall, the popular Guanghua Night Market, the Shin Kong Mitsukoshi Department Store and at least one major hotel.

Eyewitnesses and local residents reported smelling a strong gas odour about three hours before the explosions occurred. Many of them were worried and went outside.

One person wrote online that he called Kaohsiung City's hotline for residents but was told that firefighters had arrived on the scene and to go back home.

As he expressed anger to the hotline operator, he saw a large explosion. Manhole covers were blown three stories high. Many people lay injured on the street.

Another resident who lived nearby said that he thought it was an earthquake at first and then he heard something like a bomb. The electricity was cut off. He immediately woke up his wife and children and they quickly left their home.